This disclosure relates to a mechanism for providing mobility for an Internet-type protocol in a packet radio network such as General Packet Radio Service (GPRS) or Universal Mobile Telecommunications System (UMTS). An example of such an Internet-type mobility protocol is the IP mobility (IP=Internet Protocol), which is the topic of standards RFC2002 to RFC2004 and RFC2290 by the Internet Engineering Task Force (IETF). These RFC standards are incorporated herein by reference. In short, IP mobility is a mechanism for providing a mobile user with telecommunications capability using an IP address. It enables mobile nodes to change their points of attachment in the Internet without changing their IP address. Thus it facilitates the communication of a mobile node and a correspondent host with the mobile node's home address. FIG. 1 illustrates some elements of a packet radio network which are relevant to one or more embodiments.
Within the context of this application, “Network Access Server” (NAS) is a device providing users with temporary, on-demand network access. This access is point-to-point using telephone, ISDN or cellular connections, etc. “Mobile Node” (MN) refers to a host that wants to use a Home Network address while physically connected by a point-to-point link (phone line, ISDN, etc.) to a NAS that does not reside on the Home Network. Mobile Station” (MS) is a mobile node having a radio interface to the network. A “Tunnel” is the path followed by a datagram when encapsulated. The model of a tunnel is such that, while encapsulated, a datagram is routed to a known decapsulation agent, which decapsulates the datagram and then correctly delivers it to its ultimate destination. Each mobile node connecting to a home agent does so over a unique tunnel, identified by a tunnel identifier which is unique to a given Foreign Agent/Home Agent pair.
A “Home Network” is the IP network to which a user logically belongs. Physically, it can be e.g., a local area network (LAN) connected via a router to the Internet. A “Home Address” is an address that is assigned to a mobile node for an extended period of time. It may remain unchanged regardless of where the MN is attached to the Internet. Alternatively, it could be assigned from a pool of addresses. A “Home Agent” is a routing entity in a mobile node's home network which tunnels packets for delivery to the mobile node when it is away from home, and maintains current location information for the mobile node. The home agent tunnels datagrams for delivery to, and, optionally, detunnels datagrams from, a mobile node when the mobile node is away from home.
A “Foreign Agent” refers to a routing entity on a mobile node's visited network which provides routing services to the mobile node while registered, thus allowing a mobile node to utilize its home network address. The foreign agent detunnels and delivers packets to the mobile node that were tunnelled by the mobile node's home agent. For datagrams sent by a mobile node, the foreign agent may serve as a default router for registered mobile nodes.
RFC2002 defines “Care-of-Address” (COA) as the termination point of a tunnel toward a mobile node, for datagrams forwarded to the mobile node while it is away from home. The protocol can use two different types of care-of-address: a “foreign agent care-of-address” is an address announced by a foreign agent with which the mobile node is registered, and a “co-located care-of-address” is an externally obtained local address which the mobile node has acquired in the network. Within the context of this application, “Care-of-Address” (COA) is an announced address of a foreign agent with which the mobile node is registered. An MN may have several COAs at the same time.
An MN's COA is registered with its “Home Agent” (HA). The list of COAs is updated when the mobile node receives advertisements from foreign agents. If an advertisement expires, its entry or entries should be deleted from the list. One foreign agent can provide more than one COA in its advertisements. “Mobility Binding” is the association of a home address with a care-of-address, along with the remaining lifetime of that association. An MN registers its COA with its HA by sending a Registration Request. The HA replies with a Registration Reply and retains a binding for the MN.
Routing data packets to an MN is a problem in a packet radio network, such as GPRS. This is because the data network address of the MN typically has a static routing mechanism, whereas a MN can roam from one subnetwork to another. One approach for data packet routing in a mobile environment is the concept of Mobile IP. Mobile IP enables the routing of IP datagrams to mobile hosts, independent of the point of attachment in the subnetwork. The standard Mobile IP concept does not fit exactly in the GPRS environment because network protocols other than IP must be supported too.
Also, mobility management within a GPRS network is based on mechanisms different from Mobile IP, which is only defined for the Internet Protocol.
The GPRS infrastructure comprises support nodes such as a “gateway GPRS support node” (GGSN) and a “serving GPRS gateway support node” (SGSN).
The main functions of the GGSN nodes involve interaction with the external data network. The GGSN updates the location directory using routing information supplied by the SGSNs about an MS's path and routes the external data network protocol packet encapsulated over the GPRS backbone to the SGSN currently serving the MS. It also decapsulates and forwards external data network packets to the appropriate data network and handles the billing of data traffic.
The main functions of the SGSN are to detect new GPRS mobile stations in its service area, handle the process of registering the new MSs along with the GPRS registers, send/receive data packets to/from the GPRS MS, and keep a record of the location of the MSs inside of its service area.
The subscription information is stored in a GPRS “Home Location Register” (HLR) where the mapping between a mobile's identity (such as MS-ISDN or IMSI) and the PSPDN address is stored. The GPRS register acts as a database from which an SGSN can ask whether a new MS in its area is allowed to join the GPRS network.
The GPRS gateway support nodes GGSN connect an operator's GPRS network to external systems, such as other operators' GPRS systems, data networks 11, such as an IP network (Internet) or an X.25 network, and service centers. Fixed hosts 14 can be connected to the data network 11 e.g. by means of a local area network LAN and a router 15. A border gateway BG provides access to an inter-operator GPRS backbone network 12. The GGSN may also be connected directly to a private corporate network or a host. The GGSN includes GPRS subscribers' “Packet Data Protocol” (PDP) addresses and routing information, i.e. SGSN addresses. Routing information is used for tunneling protocol data units PDU from the data network 11 to the current switching point of the MS, i.e. to the serving SGSN. The functionalities of the SGSN and GGSN can be connected to the same physical node.
The home location register HLR of the GSM network contains GPRS subscriber data and routing information and it maps the subscriber's “International Mobile Subscriber Identity” (IMSI) into one or more pairs of PDP type and PDP address. The HLR also maps each PDP type and PDP address pair into a GGSN node. The SGSN has a Gr interface to the HLR (a direct signaling connection or via an internal backbone network 13). The HLR of a roaming MS and its serving SGSN may be in different mobile communication networks.
The intra-operator backbone network 13, which interconnects an operator's SGSN and GGSN equipment, can be implemented, for example by means of a local network, such as an IP network. It should be noted that an operator's GPRS network can also be implemented without the intra-operator backbone network, e.g., by providing all features in one computer.
A GPRS network in its current form is able to support IP mobility if an MS implements the Mobile IP protocol and if it has a private IP address assigned by some company or internet service provider (ISP). When a GGSN node assigns a temporary IP address to the MS, the MS can use this temporary address as its care-of-address (COA) and register the address with its home agent, thus benefiting from the Mobile IP services. This is also true when the MS is using a predefined GGSN IP address, which can also be regarded as a COA.
A problem of the temporary and predefined GGSN-assigned IP addresses in the known IP mobility mechanisms is that they consume valuable IPv4 address space because an MS requires two IP addresses, one from its home network and another one from the visited network. Moreover, the tunneling requires that IP packets are sent to the MS using Mobile IP encapsulation, which wastes precious radio resources.